WO 2005/032712 discloses a method for preparing rhodium phosphine complexes comprising the steps of (a) dissolving Rh(diolefin)(acac) in one or more ethereal solvents, in particular strongly coordinating tetrahydrofuran (THF), optionally with dialkyl ethers such as methyl tert-butyl ether (MTBE) (b) adding to this a fluorinated non-mineral acid HX, such as a tetrafluoroboric acid etherate, and alcohol solvent or alcohol containing solvent mixture, either simultaneously or sequentially, to form a soluble solvated complex of rhodium with one or more of the reaction solvents, (c) adding the phosphorus ligand, either in solution in an organic solvent or neat, and (d) collecting the crystalline precipitate.